These are my cycles render times:
CPU: Intel i7 3.5ghz
GPU: Nvidia GTX 1070
GPU
960 x 540 render
Time: 1 min 9 sec 1920x1080
Time: 1 min 0 sec 480x540
Time: 1 min 1 sec 512x512
Time: 59 sec 480x270
Time: 1 min 4 sec 256x256
Time: 1 min 20 sec 128x128
Time: 2 min 49 sec 64x64
CPU
Time: 5 min 37 sec 128x128
Time: 5 min 6 sec 64x64